Abstract:

The present invention provides standing wave fluidic and biological tools,
including: at least one elongated fiber that has mesoscale (i.e.
milliscale), microscale, nanoscale, or picoscale dimensions, the at least
one elongated fiber having a first end and a second end; and an actuator
coupled to the first end of the at least one elongated fiber, wherein the
actuator is operable for applying oscillation cycles to the at least one
elongated fiber in one or more directions, and wherein the actuator is
operable for generating a standing wave in the at least one elongated
fiber. These standing wave fluidic and biological tools are selectively
disposed in a fluid to provide a function such as mixing the fluid,
measuring the viscosity of the fluid, attracting particles in the fluid,
shepherding particles in the fluid, providing propulsive force in the
fluid, pumping the fluid, dispensing the fluid, sensing particles in the
fluid, and detecting particles in the fluid, among others.

Claims:

1. A standing wave tool, comprising:at least one elongated fiber that has
small scale dimensions, the at least one elongated fiber comprising at
least a first end and a second end; andan actuator directly or indirectly
coupled to the first end of the at least one elongated fiber,wherein the
actuator is operable for applying oscillation cycles to the at least one
elongated fiber in one or more directions, andwherein the actuator is
operable for generating a standing wave in the at least one elongated
fiber.

2. The standing wave tool of claim 1, wherein the second end of the at
least one elongated fiber is unconstrained.

3. The standing wave tool of claim 1, wherein the second end of the at
least one elongated fiber is constrained.

4. The standing wave tool of claim 1, wherein the at least one elongated
fiber is constrained between the first end and the second end.

5. The standing wave tool of claim 1, further comprising:an actuator
directly or indirectly coupled to the second end of the at least one
elongated fiber,wherein the actuator is operable for applying oscillation
cycles to the at least one elongated fiber in one or more directions,
andwherein the actuator is operable for generating a standing wave in the
at least one elongated fiber.

6. The standing wave tool of claim 1, wherein the at least one elongated
fiber comprises one of a substantially rod-like structure, a
substantially beam-like structure, a substantially tube-like structure, a
substantially planar structure, a structure of varying cross-section, a
biological structure, and a combination thereof.

7. The standing wave tool of claim 1, wherein the at least one elongated
fiber comprises a composite structure comprising a plurality of materials
or one material comprising a plurality of properties.

8. A method for utilizing a standing wave tool in a fluidic and/or
biological environment, comprising:providing at least one elongated fiber
that has small scale dimensions, the at least one elongated fiber
comprising at least a first end and a second end;providing an actuator
directly or indirectly coupled to the first end of the at least one
elongated fiber,wherein the actuator is operable for applying oscillation
cycles to the at least one elongated fiber in one or more directions,
andwherein the actuator is operable for generating a standing wave in the
at least one elongated fiber; anddisposing at least a portion of the at
least one elongated fiber in a fluid.

9. The method for utilizing a standing wave tool of claim 8, wherein the
second end of the at least one elongated fiber is unconstrained.

10. The method for utilizing a standing wave tool of claim 8, wherein the
second end of the at least one elongated fiber is constrained.

11. The method for utilizing a standing wave tool of claim 8, wherein the
at least one elongated fiber is constrained between the first end and the
second end.

12. The method for utilizing a standing wave tool of claim 8, further
comprising:providing an actuator directly or indirectly coupled to the
second end of the at least one elongated fiber,wherein the actuator is
operable for applying oscillation cycles to the at least one elongated
fiber in one or more directions, andwherein the actuator is operable for
generating a standing wave in the at least one elongated fiber.

13. The method for utilizing a standing wave tool of claim 8, wherein the
at least one elongated fiber comprises one of a substantially rod-like
structure, a substantially beam-like structure, a substantially tube-like
structure, a substantially planar structure, a structure of varying
cross-section, a biological structure, and a combination thereof.

14. The method for utilizing a standing wave tool of claim 8, wherein the
at least one elongated fiber comprises a composite structure comprising a
plurality of materials or one material comprising a plurality of
properties.

15. The method for utilizing a standing wave tool of claim 8, further
comprising quantifying a change in a frequency response function of the
at least one elongated fiber.

16. The method for utilizing a standing wave tool of claim 8, wherein the
at least one elongated fiber provides a function selected from the group
consisting of mixing the fluid, measuring the viscosity of the fluid,
attracting particles in the fluid, shepherding particles in the fluid,
providing propulsive force in the fluid, pumping the fluid, dispensing
the fluid, sensing particles in the fluid, detecting particles in the
fluid, measuring a mechanical stiffness of particles in the fluid,
wicking the fluid, and wicking particles in the fluid.

17. The method for utilizing a standing wave tool of claim 8, further
comprising disposing at least a portion of the at least one elongated
fiber concentrically within a channel structure.

18. The method for utilizing a standing wave tool of claim 8, further
comprising removing at least a portion of the at least one elongated
fiber from the fluid.

19. A standing wave tool, comprising:at least one elongated fiber that has
small scale dimensions, the at least one elongated fiber comprising at
least a first end and a second end;an actuator directly or indirectly
coupled to the first end of the at least one elongated fiber,wherein the
actuator is operable for applying oscillation cycles to the at least one
elongated fiber in one or more directions, andwherein the actuator is
operable for generating a standing wave in the at least one elongated
fiber; anda receptor material disposed on a surface of the at least one
elongated fiber,wherein the receptor material is operable for interacting
with a target material disposed in a fluid.

20. The standing wave tool of claim 19, wherein a frequency response
function of the at least one elongated fiber changes when the receptor
material interacts with the target material.

21. The standing wave tool of claim 19, wherein the receptor material
comprises a first biomolecule and the target material comprises a second
biomolecule.

22. A method for utilizing a standing wave tool in a fluidic and/or
biological environment, comprising:providing at least one elongated fiber
that has small scale dimensions, the at least one elongated fiber
comprising a first end and a second end;providing an actuator directly or
indirectly coupled to the first end of the at least one elongated
fiber,wherein the actuator is operable for applying oscillation cycles to
the at least one elongated fiber in one or more directions, andwherein
the actuator is operable for generating a standing wave in the at least
one elongated fiber; andproviding a receptor material disposed on a
surface of the at least one elongated fiber,wherein the receptor material
is operable for interacting with a target material disposed in a fluid.

23. The method for utilizing a standing wave tool of claim 22, further
comprising obtaining a frequency response function of the at least one
elongated fiber before and after the receptor material interacts with the
target material.

24. The method for utilizing a standing wave tool of claim 22, wherein the
receptor material comprises a first biomolecule and the target material
comprises a second biomolecule.

25. The method for utilizing a standing wave tool of claim 22, further
comprising capturing the target material with the at least one elongated
fiber.

26. The method for utilizing a standing wave tool of claim 25, further
comprising wicking the target material along the at least one elongated
fiber.

27. The method for utilizing a standing wave tool of claim 22, further
comprising using an external method for detecting the presence of the
target material on the at least one elongated fiber.

Description:

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001]The present non-provisional patent application claims the benefit of
priority of U.S. Provisional Patent Application No. 61/031,901, filed on
Feb. 27, 2008, and entitled "STANDING WAVE FLUIDIC AND BIOLOGICAL TOOLS;"
U.S. Provisional Patent Application No. 61/054,660, filed on May 20,
2008, and entitled "STANDING WAVE FLUIDIC AND BIOLOGICAL TOOLS;" U.S.
Provisional Patent Application No. 61/122,535, filed on Dec. 15, 2008,
and entitled "MICROSCALE LIQUID HANDLING AND MICROMIXING DEVICE FOR ALL
HIGH THROUGHPUT DRUG DISCOVERY PROCESSES;" and U.S. Provisional Patent
Application No. 61/122,518, also filed on Dec. 15, 2008, and entitled
"STANDING WAVE SENSOR FOR VISCOMETRY AND RHEOLOGY OF MICROSAMPLES;" the
contents of all of which are incorporated in full by reference herein.
The present non-provisional patent application is a continuation-in-part
of co-pending U.S. patent application Ser. No. 11/956,915, filed on Dec.
14, 2007, and entitled "MULTI-DIMENSIONAL STANDING WAVE PROBE FOR
MICROSCALE AND NANOSCALE MEASUREMENT, MANIPULATION, AND SURFACE
MODIFICATION," the contents of which are also incorporated in full by
reference herein. U.S. patent application Ser. No. 11/956,915 claims the
benefit of priority of U.S. Provisional Patent Application Nos.
60/874,772, filed on Dec. 14, 2006, and entitled "MULTI-DIMENSIONAL
STANDING WAVE SENSOR WITH AN APPLICATION TO DIESEL MANUFACTURING" and
60/931,724, filed on May 25, 2007, and entitled "STANDING WAVE PROBES FOR
MEASUREMENT, MANIPULATION, AND MODIFICATION ACROSS DIMENSIONAL SCALES,"
the contents of both of which are further incorporated in full by
reference herein. U.S. patent application Ser. No. 11/956,915 is a
continuation in part of co-pending U.S. patent application Ser. No.
11/818,669, filed on Jun. 15, 2007, and entitled "SELF-SENSING TWEEZER
DEVICES AND ASSOCIATED METHODS FOR MICRO AND NANOSCALE MANIPULATION AND
ASSEMBLY," which claims the benefit of priority of U.S. Provisional
Patent Application Nos. 60/813,962, filed on Jun. 15, 2006, and entitled
"SELF-SENSING TWEEZERS FOR MICRO-ASSEMBLY AND MANIPULATION" and
60/931,724, filed on May 25, 2007, and entitled "STANDING WAVE PROBES FOR
MEASUREMENT, MANIPULATION, AND MODIFICATION ACROSS DIMENSIONAL SCALES,"
the contents of all of which are still further incorporated in full by
reference herein. U.S. patent application Ser. No. 11/818,669 is a
continuation-in-part of previously co-pending U.S. patent application
Ser. No. 10/989,744 (now U.S. Pat. No. 7,278,297), filed on Nov. 16,
2004, and entitled "AN OSCILLATING PROBE WITH A VIRTUAL PROBE TIP," which
claims the benefit of priority of U.S. Provisional Patent Application No.
60/520,500, filed on Nov. 17, 2003, and entitled "AN OSCILLATING PROBE
WITH A VIRTUAL PROBE TIP," the contents of both of which are still
further incorporated in full by reference herein.

FIELD OF THE INVENTION

[0002]The present invention relates generally to the mesoscale (i.e.
milliscale), microscale, nanoscale, and picoscale technology fields. More
specifically, the present invention relates to standing wave fluidic and
biological tools that may be used in liquid, gas, solid state,
multi-phase, and viscoelastic environments and combinations thereof These
standing wave fluidic and biological tools have a wide range of novel
applications of great importance to a variety of industries.

BACKGROUND OF THE INVENTION

[0003]Commonly assigned U.S. Pat. No. 7,278,297 (Bauza et al.) provides an
oscillating probe including an elongated rod having a first free end and
a second end that is attached to an actuator that applies oscillation
cycles to the elongated rod. The oscillation of the elongated rod during
at least one complete oscillation cycle of the actuator causes the free
end to move in at least a one-dimensional envelope, producing a defined
virtual probe tip at the free end. The shape of this virtual probe tip is
defined by both the characteristic shape of the oscillation of the free
end and the geometry of the elongated rod. This oscillating probe may be
used in microscale and nanoscale measurement, manipulation, and/or
surface modification applications, for example.

[0004]Similarly, commonly assigned U.S. patent application Ser. No.
11/956,915 (Woody et al.) provides a multi-dimensional standing wave
probe for microscale and nanoscale measurement, manipulation, and/or
surface modification applications including a filament having a first
free end and a second end that is attached to an actuator that applies
oscillation cycles to the filament. The oscillation of the filament
during at least one complete oscillation cycle of the actuator causes the
free end to move in a multi-dimensional envelope, producing a defined
virtual probe tip at the free end. The shape of this virtual probe tip is
defined by both the characteristic shape of the oscillation of the free
end and the geometry of the filament.

[0005]The principles of operation of this oscillating probe and
multi-dimensional standing wave probe--namely the generation of a
standing wave in a mesoscale (i.e. milliscale), microscale, nanoscale, or
picoscale fiber and, optionally, the formation of a virtual probe
tip--may be utilized in a wide range of novel applications of great
importance to a variety of industries. The most promising of these novel
applications include fluidic and biological applications that involve
liquid, gas, solid state, multi-phase, and viscoelastic environments and
combinations thereof, as described in greater detail herein.

BRIEF SUMMARY OF THE INVENTION

[0006]In various exemplary embodiments, the present invention provides
novel uses for the standing wave probes of U.S. Pat. No. 7,279,297 (Bauza
et al.) and U.S. patent application Ser. No. 11/956,915 (Woody et al.),
especially in fluidic and biological applications that involve liquid,
gas, solid state, multi-phase, and viscoelastic environments and
combinations thereof. As described in greater detail herein, these
standing wave probes typically include a high-aspect ratio mesoscale
(i.e. milliscale), microscale, nanoscale, or picoscale fiber that is
directly or indirectly coupled to at least one actuator that applies
oscillation cycles to the fiber, generating a standing wave in the fiber.
The fiber may be constrained at one end, causing a virtual probe tip to
be formed at the free end, or it may be constrained at both ends. In the
later case, an actuator may be coupled to one or both ends of the fiber.
Intervening constraints along the length of the fiber are also
contemplated herein. In any case, the standing wave generated in the
fiber is defined by both the characteristic shape of the oscillation
cycles applied by the actuator(s) and the geometry of the fiber. The
standing wave generated in the fiber may be along the longitudinal,
lateral, or torsional direction of the fiber, or may produce a
semicircular motion around the axis of rotation of the fiber, for
example, resulting in spiral like movements that are a combination of
lateral and torsional motions. Higher harmonic modes generated in the
fiber produce higher potential and kinetic energy. Multiple standing wave
probes, individually or collectively utilizing multiple fibers, may also
be utilized in concert, as the configurations and methodologies of the
present invention are very robust.

[0007]In one exemplary embodiment, the present invention provides a
standing wave tool, including: at least one elongated fiber that has
mesoscale dimensions or smaller, the at least one elongated fiber
including at least a first end and a second end; and an actuator directly
or indirectly coupled to the first end of the at least one elongated
fiber, wherein the actuator is operable for applying oscillation cycles
to the at least one elongated fiber in one or more directions, and
wherein the actuator is operable for generating a standing wave in the at
least one elongated fiber. Optionally, the second end of the at least one
elongated fiber is unconstrained. Optionally, the second end of the at
least one elongated fiber is constrained. Optionally, the at least one
elongated fiber is constrained between the first end and the second end.
Optionally, the standing wave tool also includes: an actuator directly or
indirectly coupled to the second end of the at least one elongated fiber,
wherein the actuator is operable for applying oscillation cycles to the
at least one elongated fiber in one or more directions, and wherein the
actuator is operable for generating a standing wave in the at least one
elongated fiber. Preferably, the at least one elongated fiber is one of a
substantially rod-like structure, a substantially beam-like structure, a
substantially tube-like structure, a substantially planar structure, a
structure of varying cross-section, a biological structure, and a
combination thereof. Optionally, the at least one elongated fiber is a
composite structure comprising a plurality of materials, such as a base
material and a deposited or bonded material, or one material comprising a
plurality of properties.

[0008]In another exemplary embodiment, the present invention provides a
method for utilizing a standing wave tool in a fluidic and/or biological
environment, including: providing at least one elongated fiber that has
mesoscale dimensions or smaller, the at least one elongated fiber
including at least a first end and a second end; providing an actuator
directly or indirectly coupled to the first end of the at least one
elongated fiber, wherein the actuator is operable for applying
oscillation cycles to the at least one elongated fiber in one or more
directions, and wherein the actuator is operable for generating a
standing wave in the at least one elongated fiber; and disposing at least
a portion of the at least one elongated fiber in a fluid. Optionally, the
second end of the at least one elongated fiber is unconstrained.
Optionally, the second end of the at least one elongated fiber is
constrained. Optionally, the at least one elongated fiber is constrained
between the first end and the second end. Optionally, the method for
utilizing the standing wave tool also includes: providing an actuator
directly or indirectly coupled to the second end of the at least one
elongated fiber, wherein the actuator is operable for applying
oscillation cycles to the at least one elongated fiber in one or more
directions, and wherein the actuator is operable for generating a
standing wave in the at least one elongated fiber. Preferably, the at
least one elongated fiber is one of a substantially rod-like structure, a
substantially beam-like structure, a substantially tube-like structure, a
substantially planar structure, a structure of varying cross-section, a
biological structure, and a combination thereof. Optionally, the at least
one elongated fiber is a composite structure comprising a plurality of
materials, such as a base material and a deposited or bonded material, or
one material comprising a plurality of properties. Optionally, the method
for utilizing the standing wave tool further includes quantifying a
change in a frequency response function of the at least one elongated
fiber. As contemplated herein, the at least one elongated fiber provides
a function selected from the group consisting of mixing the fluid,
measuring the viscosity of the fluid, attracting particles in the fluid,
shepherding particles in the fluid, providing propulsive force in the
fluid, pumping the fluid, dispensing the fluid, sensing particles in the
fluid, detecting particles in the fluid, measuring a mechanical stiffness
of particles in the fluid, wicking the fluid, and wicking particles in
the fluid. Optionally, the method for utilizing the standing wave tool
still further includes disposing at least a portion of the at least one
elongated fiber concentrically within a channel structure. Optionally,
the method for utilizing the standing wave tool still further includes
removing at least a portion of the at least one elongated fiber from the
fluid.

[0009]In a further exemplary embodiment, the present invention provides a
standing wave tool, including: at least one elongated fiber that has
mesoscale dimensions or smaller, the at least one elongated fiber
including a first end and a second end; an actuator directly or
indirectly coupled to the first end of the at least one elongated fiber,
wherein the actuator is operable for applying oscillation cycles to the
at least one elongated fiber in one or more directions, and wherein the
actuator is operable for generating a standing wave in the at least one
elongated fiber; and a receptor material disposed on a surface of the at
least one elongated fiber, wherein the receptor material is operable for
reacting with a target material disposed in a fluid, and wherein a
frequency response function of the at least one elongated fiber changes
when the receptor material reacts with the target material, thereby
detecting/sensing the target material. Optionally, the receptor material
is a biomolecule, such as an antibody, and the target material is a
biomolecule, such as an antigen. In this exemplary embodiment, it should
be noted that the target material may be attracted to the receptor
material via surface tension and then wicked along the elongated
fiber(s), for example. As an alternative, the target material may simply
be attracted to and held by the elongated fiber(s), and then be detected
by another external methodology, such as fluorescing, etc.

[0010]In a still further exemplary embodiment, the present invention
provides a method for utilizing a standing wave tool in a fluidic and/or
biological environment, including: providing at least one elongated fiber
that has mesoscale dimensions or smaller, the at least one elongated
fiber including a first end and a second end; providing an actuator
coupled to the first end of the at least one elongated fiber, wherein the
actuator is operable for applying oscillation cycles to the at least one
elongated fiber in one or more directions, and wherein the actuator is
operable for generating a standing wave in the at least one elongated
fiber; providing a receptor material disposed on a surface of the at
least one elongated fiber, wherein the receptor material is operable for
reacting with a target material disposed in a fluid; and measuring a
frequency response function of the at least one elongated fiber before
and after the receptor material reacts with the target material, thereby
detecting/sensing the target material. Optionally, the receptor material
is a biomolecule, such as an antibody, and the target material is a
biomolecule, such as an antigen.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]The present invention is illustrated and described herein with
reference to the various drawings, in which like reference numbers are
used to denote like device components/method steps, as appropriate, and
in which:

[0012]FIG. 1 is a schematic diagram illustrating one exemplary embodiment
of the standing wave sensor of the present invention, the standing wave
sensor having a constrained end and a free end;

[0013]FIG. 2 is a schematic diagram illustrating another exemplary
embodiment of the standing wave sensor of the present invention, the
standing wave sensor having two constrained ends;

[0014]FIG. 3 is a schematic diagram illustrating one exemplary embodiment
of the standing wave sensors of the present invention used in a mixing
application;

[0015]FIG. 4 is a schematic diagram illustrating one exemplary embodiment
of the standing wave sensors of the present invention used in an
attracting and shepherding application;

[0016]FIG. 5 is a schematic diagram illustrating one exemplary embodiment
of the standing wave sensors of the present invention used in a uni or
multi-directional fluid pumping and dispensing (i.e. flow directing)
application;

[0017]FIG. 6 is a schematic diagram illustrating one exemplary embodiment
of the standing wave sensors of the present invention used in a
biosensing application;

[0018]FIG. 7 is a schematic diagram illustrating one exemplary embodiment
of a sequenced method, using appropriate nanopositioners or the like,
involving the insertion of the standing wave probes of the present
invention into and removal of the standing wave probes of the present
invention from a series of fluid filled wells or the like; and

[0019]FIG. 8 is a schematic diagram illustrating one exemplary embodiment
of a sequenced method, using appropriate nanopositioners or the like,
involving the insertion of arrays of the standing wave probes of the
present invention into and removal of arrays of the standing wave probes
of the present invention from a series of arrays fluid filled wells or
the like.

DETAILED DESCRIPTION OF THE INVENTION

[0020]Again, in various exemplary embodiments, the present invention
provides novel uses for the standing wave probes of U.S. Pat. No.
7,279,297 (Bauza et al.) and U.S. patent application Ser. No. 11/956,915
(Woody et al.), especially in fluidic and biological applications that
involve liquid, gas, solid state, multi-phase, and viscoelastic
environments and combinations thereof. As described in greater detail
herein, these standing wave probes typically include a high-aspect ratio
mesoscale (i.e. milliscale), microscale, nanoscale, or picoscale fiber
that is directly or indirectly coupled to at least one actuator that
applies oscillation cycles to the fiber, generating a standing wave in
the fiber. The fiber may be constrained at one end, causing a virtual
probe tip to be formed at the free end, or it may be constrained at both
ends. In the later case, an actuator may be coupled to one or both ends
of the fiber. Intervening constraints along the length of the fiber are
also contemplated herein. In any case, the standing wave generated in the
fiber is defined by both the characteristic shape of the oscillation
cycles applied by the actuator(s) and the geometry of the fiber. The
standing wave generated in the fiber may be along the longitudinal
direction of the fiber, or may produce a semicircular motion around the
axis of rotation of the fiber, for example, resulting in spiral like
movements. Higher harmonic modes generated in the fiber produce higher
potential and kinetic energy. Multiple standing wave probes may also be
utilized in concert, as the configurations and methodologies of the
present invention are very robust.

[0021]Referring to FIG. 1, in one exemplary embodiment, the standing wave
sensor 10 of the present invention includes a high-aspect ratio mesoscale
(i.e. milliscale), microscale, nanoscale, or picoscale fiber 12 that is
coupled to at least one actuator 14 that applies oscillation cycles to
the fiber 12, generating a standing wave 16 in the fiber 12. In this
exemplary embodiment, the actuator 14 represents a constraint at one end,
causing a virtual probe tip 18 to be formed at the free end. The actuator
14 may be, for example, a piezoelectric crystal actuator or the like
including a plurality of thin flexure structures coupled to a plurality
of electrodes. The actuator 14 may also be, for example, a non-mechanical
actuator, such as pulsed light or other energetic waves used to actuate a
carbon nanotube or the like. In such a case, the system for measuring the
fiber response could be separate from the actuation system. All actuation
methods that are capable of generating a standing wave in the fiber 12
are contemplated herein.

[0022]This technological platform is capable of operating as a combined
sensor for detecting surface contact (physical or non-physical),
self-sensing tweezers for grasping and releasing a component, an energy
source for performing surface modification, and as described herein.
Single and multi-dimensional standing waves are propagated at a rate on
the order of kHz to MHz along the fiber 12. The magnitude of energy
contained within the "wave packet" as compared to the
flexibility/stiffness of the fiber 12 enables a pronounced single or
multi-dimensional standing wave to be generated and sustained along the
fiber 12. This "wave packet" is defined as an envelope containing an
arbitrary number of waveforms that each have a specific position and
momentum. As a result of the periodic energy transferred to the fiber 12,
the combined energy arriving at and reflecting from the tip of the fiber
12 generates single or multi-dimensional geometrical patterns (such as
hemispheres, ellipsoids, and other Lissajous-type shapes). The shape of
the virtual probe tip 18 may be changed, where programmability is a
function of the synchronization, magnitude, and modal shapes produced by
the standing waves.

[0023]A time averaged picture of the oscillating fiber 12 produces an
image of the oscillating standing wave sensor 10 as a solid volume traced
out by the path of the outer surface of the fiber 12 that has a defined
geometrical pattern. The standing wave probe 10 consists of the fiber 12;
however, the virtual probe tip 18 consists of an integral of the path
produced by the oscillating tip of the fiber 12. The outer locus of the
virtual probe tip 18 consists of the total sum of motion produced by the
very end of the fiber 12, thereby generating a pseudo field capable of
interacting with other solids, surfaces, and fluids in near proximity.
This programmable pseudo field (i.e. the virtual probe tip 18) may be
employed across a wide variety of applications. It should be noted that
the "virtual envelope" not including the virtual probe tip 18 behaves and
may be used in the same manner. It should be noted that the advantage of
the present technology is that the amplitude of the standing wave
generated in the fiber is relatively great as compared to the dimensions
of the fiber 12, which may have a given degree of rigidity such that it
is described as "rigid," "semi-rigid," or "flexible." This provides a
great deal of potential and kinetic energy, such that the standing wave
may be sustained relatively uninterrupted, even when disposed in a fluid.

[0024]As used herein, the terms "sensor," "probe," and the like are used
interchangeably, and may imply devices that are actuated and may or may
not provide sensing capability, depending upon the specific application
involved. The present invention contemplates any and all arrayed uses of
the "probes" described herein, in any and all orientation(s). Such
arrayed uses are application specific. As used herein, the terms
"elongated rod," "filament," "fiber," and the like are also used
interchangeably, and may be extended to include other thin films and
high-aspect ratio mesoscale (i.e. milliscale), microscale, nanoscale, or
picoscale structures. In fact, any mesoscale (i.e. milliscale),
microscale, nanoscale, or picoscale structure--non-biological or
biological--in which a standing wave may be generated is contemplated
herein, regardless of its configuration. For example, the "fiber" may be
a substantially rod-like structure, a substantially beam-like structure,
a substantially tube-like structure, a substantially planar structure, or
a structure of varying cross-section. It may be one of these structures
with one or more other structures, such as one or more carbon nanotubes
or the like, grown on it in order to increase its effective surface area.
It may simply be a biological structure, such as a flagellum or the like,
grown on an oscillator, or a mass of such biological structures. As used
herein, the term "fluid" is used to refer to any liquid, gas, solid
state, multi-phase, or viscoelastic environment or combination thereof,
all of which are used interchangeably. The standing wave tools of the
present invention may be used in any environment in which, in the most
basic sense, interaction with one or more particles causes a change in
the associated signal, allowing the tools to interact with the
particle(s), whether or not signal feedback is utilized (i.e. the
standing wave tools may be utilized for their physical functionality, and
do not necessarily need to provide sensing signal, as the resulting
particle interactions could be explored using optics, etc.).

[0025]Referring to FIG. 2, in another exemplary embodiment, the standing
wave sensor 20 of the present invention includes a high-aspect ratio
mesoscale (i.e. milliscale), microscale, nanoscale, or picoscale fiber 12
that is coupled to at least one actuator 14 that applies oscillation
cycles to the fiber 12, generating a standing wave 16 in the fiber 12. In
this exemplary embodiment, the actuators 14 represent constraints at both
ends. The actuators 14 may be, for example, piezoelectric crystal
actuators or the like including a plurality of thin flexure structures
coupled to a plurality of electrodes. The actuators 14 may also be, for
example, non-mechanical actuators, such as pulsed light or other
energetic waves used to actuate a carbon nanotube or the like. In such a
case, the system for measuring the fiber response could be separate from
the actuation system. All actuation methods that are capable of
generating a standing wave in the fiber 12 are contemplated herein. In an
alternative exemplary embodiment, an actuator 14 may be used at one end,
while the other end is "fixed." Intervening constraints along the length
of the fiber are also contemplated herein. For example, a common
actuation mechanism, disposed at a node of vibration, may be disposed
between and/or used to actuate two fibers 12 (or two portions of a single
fiber 12) in close proximity. Such a system may be constrained at each
end, constrained at one end and have a virtual tip at the other end, or
have a virtual tip at each end. All or a portion of this system may then
be immersed in the fluid.

[0026]Again, single and multi-dimensional standing waves are propagated at
a rate on the order of kHz to MHz along the fiber 12. The magnitude of
energy contained within the "wave packet" as compared to the
flexibility/stiffness of the fiber 12 enables a pronounced single or
multi-dimensional standing wave to be generated and sustained along the
fiber 12. This "wave packet" is defined as an envelope containing an
arbitrary number of waveforms that each have a specific position and
momentum.

[0028]Referring to FIG. 3, in one exemplary embodiment, the standing wave
probes 10, 20 of the present invention may be used in micromixing
applications, with the oscillating fiber 12 of one or more of the
standing wave probes 10, 20 at least partially disposed in a fluid 30,
such as a liquid or a gas. In the exemplary embodiment illustrated, a
single standing wave probe 10 having a virtual probe tip 18 is used. The
fiber 12 is oscillated in one or more directions to provide different
forms of mixing. The standing wave may be increased or decreased by
increasing or decreasing the input drive voltage to the actuator 14. As
the standing wave amplitude is varied, the rate of mixing varies.
Therefore, the rate of mixing may be controlled by the electromechanical
properties of the standing wave probe 10, or variations in the applied
frequency. The use of multiple standing wave probes 10, or multiple
fibers 12, in concert allows for more advanced mixing methodologies. The
standing wave drive frequency utilized may also be varied in order to
vary the rate or duration of the mixing. A faster standing wave enables
faster mixing rates, for example. Optionally, the standing wave probes
10, 20 of the present invention may be embedded in microchannels or
microwells and then used as micromixers. Similar to these micromixing
applications, the standing wave probes 10, 20 could be used as
microslicers.

Attracting and Shepherding Applications

[0029]Referring to FIG. 4, in one exemplary embodiment, the standing wave
probes 10, 20 of the present invention have, when actuated, been observed
to attract microspheres, other particles, and even cells, individually
32, in a liquid or gas environment 30. For example, macrophage (i.e.
mouse) cells 32 in a liquid environment 30 were observed to be attracted
to the oscillating point source when actuated. The speed or rate of
approach of these cells 32 was varied by varying the characteristics of
the standing wave 16. The motion of the cells 32 was suddenly stopped by
turning the standing wave 16 off. The cells 32 were observed to "group"
around the oscillating point source and/or tip. Attracted particles have
also been observed to be drawn to the "top" of the fiber via wicking or
the like, even out of the fluid itself, and towards/to the tuning fork
itself, allowing for much greater attraction to be achieved than that
which would be expected by the fiber alone. This same wicking is observed
with the fluid itself, various chemicals, etc. This is potentially a huge
scientific advancement. Thus, the virtual probe tip 18 may be moved to
lead cells 32 from location to location. This could have huge
implications for microscopy, cell sorting, and diagnostic applications,
among others. Other mesoscale (i.e. milliscale), microscale, nanoscale,
or picoscale particles 32 are similarly attracted to the "vacuum" (i.e.
vortex field or pressure differential) created by the standing wave
probes 10, 20 of the present invention. The longer the standing wave 16
is active, the more material is attracted to it. This could have huge
implications for a wide array of applications.

Propulsion Applications

[0030]In nature, various organisms propel themselves via a spiral movement
of a tail or the like. The energy of the potential semicircular motion
around the axis of rotation of the fiber 12 associated with the standing
wave 16, and resulting spiral like movements, may be used to propel the
standing wave probe 10 relative to a liquid or gas environment 30. One or
more fibers 12 may be excited in one or more directions to enable this
propulsion. The unique energy generated in the mesoscale (i.e.
milliscale), microscale, nanoscale, or picoscale fiber(s) 12 may be
varied in one or more directions, oscillation frequencies may be varied,
and oscillation amplitudes may be varied--all of which enable different
forms of propulsion.

Fluid Pumping and Dispensing Applications

[0031]Referring to FIG. 5, in one exemplary embodiment, the standing wave
probes 10, 20 of the present invention may be used in fluid pumping and
dispensing (i.e. flow directing) applications. The standing wave probes
10, 20 may be disposed in a micropipette or nanopipette 34. A fluid 36 is
then transferred along or across the standing wave(s) 16 and out of the
pipette 34. Preferably, when the standing wave 16 is inactive, capillary
forces prevent the fluid 36 from exiting the pipette 34. Once the
standing wave 16 is activated, an amount of energy is used to direct the
fluid 36 out of the pipette 34. Extending this further, the amount of
energy may be adjusted by varying the oscillation frequency and amplitude
of the standing wave 16. Thus, different rates of fluid expulsion may be
generated.

Cell Diagnostic Applications

[0032]The standing wave probes 10, 20 of the present invention may be used
in self-sensing biological diagnostic applications. For example, a
standing wave probe 10, 20 may be used to contact a cell and determine
the cell wall stiffness and cell viscosity. Two or more standing wave
probes 10, 20 may be used as miniature "tweezers" to squeeze a cell and
measure its characteristics. Along these lines, two or more standing wave
probes 10, 20 may be used to measure and evaluate an oocyte for invitro
fertilization, determining whether or not it is healthy and increasing
invitro fertilization yield. Standing wave probes may be used to probe
tissue to determine localized mechanical stiffness, monitor physical
changes in engineered gels, etc. For example, the standing wave probe of
the present invention is essentially a force sensor and, as such, may be
attached to a positioning device and used to track both force and
position. It could be pressed against a cell and, utilizing this force
and position information, used to characterize the localized mechanical
stiffness of the cell, etc. Such uses are too numerous to provide an
exhaustive list here.

Biosensing Applications

[0033]The standing wave methodologies of the present invention have unique
properties that enable biological sensing. More specifically, the
standing wave methodologies of the present invention enable the
diagnostic measurement of specific target biomolecules (i.e. antigens).
These biosensors may sense typical antibody-antigen binding reactions
occurring at the surface of the fiber 12. Under optimized conditions, a
crystal oscillating tuning fork resonator or the like can increase the
chances of antigen discovery if the probe is coated with an antibody
because of the increased chances of "contact."

[0034]Referring to FIG. 6, in one exemplary embodiment, the fiber 12 is
mechanically coupled to the actuator 14, such as a crystal oscillating
tuning fork resonator or the like. The combined mechanical system is
driven at the actuator's natural frequency. Depending upon the fiber's
inherent characteristics, the fiber is excited at Mode 1 or higher modes,
such as Mode 3. The actuator's oscillation amplitude creates the standing
wave 16 (FIGS. 1-5) in the fiber 12. The actuator provides both an input
signal, as well as a corresponding output signal that measures the
electromechanical response. In a classical sense, the input and output
signals may be monitored simultaneously for phase and magnitude in the
frequency domain. Thus, state-of-the-art electronics, such as lock-in
amplifiers and the like, may be used to track changes in the system's
frequency response function. For example, if the sensor tip is brought
into contact with soft tissue, the frequency response function provides
different signal characteristics. Depending upon the sensitivity of the
sensor, contacting or adding particles to the sensor changes the
frequency response function reading of the sensor. Thus, the fiber 12 may
be coated with specific receptor biomolecules 40 (i.e. antibodies) that
selectively bind with specific target biomolecules 42 (i.e. antigens),
thereby forming bound pairs 44 as the antigens 42 are attracted by the
standing wave 16, as described above. These attracted antigens 42 change
the frequency response function of the sensor as the "mass," "stiffness,"
or "energy dissipation" of the fiber 12 changes, allowing the antigens 42
to be detected and quantified.

[0035]The coating process described above (also known as
functionalization) may be uniform, patterned, or nonuniform along the
length of the fiber 12, depending upon the requirements of the biosensing
application. There are several known techniques of functionalizing a
cantilever-based biosensor. Similar approaches may be utilized to
functionalize the fiber 12 here; however, it is not obvious to anyone of
ordinary skill in the art to add functionalized receptor biomolecules 40
(i.e. antibodies) to standing wave or other novel or conventional
resonating biosensors. One unique attribute of the fiber 12 is its high
aspect ratio. This provides increased surface for the antibody-antigen
binding reaction to take place. A second advantage of this system is the
mixing effect of the standing wave biosensor 10, 20 when it is inserted
into a liquid or gas, creating a greater probability that a target
biomolecule 42 will come into contact with and therefore attach to a
receptor biomolecule 40 on the surface of the fiber 12. As a result,
antigens 42 that attach to the standing wave biosensor 10, 20 are more
readily measured in a very small volume of liquid, for example.

[0036]Once the standing wave biosensor 10, 20 is functionalized with the
receptor biomolecules 40 on its surface, the complete unit may be
inserted into a liquid environment containing the target biomolecules 42
for detection. Once inserted into the liquid environment, the standing
wave's energy generates vortices in the liquid environment, which allows
the surface of the fiber 12 to come into close contact with the target
biomolecules 42 and causes the target biomolecules 42 to be attracted and
finally attached to the surface of the activated sensing element by
antibody-antigen reaction. This form of activated attraction is referred
to as bioshepherding.

[0037]Once the antigens 42 are attached, the standing wave biosensor's
frequency response function changes as a result of the antigens 42 that
are attached. This change may be measured in or out of the liquid
environment. One possible method is to extract the standing wave
biosensor 10, 20 out of the liquid environment with the antigens 42
attached to the antibodies 40. The antigens 42 may be dried and the
sensor element activated to detect changes to the frequency response
function.

[0038]Biosensing with a composite fiber 12 is also contemplated herein. If
the fiber 12 is made of more than one material, the antibody-antigen
reaction occurring at the surface of the fiber 12 will cause differential
bending, which will change the frequency response function even more,
aiding the detection process by amplifying the changes in the frequency
response function. In a simpler version of this application, the standing
wave sensor 10, 20 of the present invention may be used as a moisture
sensor, indicating how much moisture is absorbed into and attached
receptor material. In this exemplary application, it should be noted that
the target material may be attracted to the receptor material via surface
tension and then wicked along the elongated fiber(s) for collection, for
example. As an alternative, the target material may simply be attracted
to and held by the elongated fiber(s), and then be detected by another
external methodology, such as fluorescing, etc. It should be noted that
in this and other applications, the probe of the present invention may be
inserted into a fluid for cleaning or surface preparation, for example,
in the case of functionalization, and it may be removed from the fluid
for shaking off attached fluid and particles, and accelerating drying,
oxidation, and/or other reactions of the adhered particles or films.

[0039]The present invention provides a low frequency modulation device
equipped with microscale fibers or the like. These fibers, when
modulated, produce a pronounced mechanical wave that propagates back and
forth in the ultrasonic frequency range. A change in modulation allows
for the detection of attachment. Increasing specificity of the agent to
bind is done by covalent attachment of a receptor, such as an antibody
(as described above) or other protein, to the fiber. Thus, the present
invention provides an analytic detection system that is capable of
identifying and quantifying agents of interest, in general. The device
consists of a specially coated fiber vibrating at low frequency that
detects the binding of agents to the fiber by changes in the oscillation
of the fiber.

[0040]Many proteins serve as natural receptors of specific ligands and
have a degree of specificity and affinity to allow for development of a
detection method for these ligands. For example, antibodies against
microbes may be designed that recognize a specific organism and many
membrane receptors may recognize a specific biological component.
Oftentimes, these proteins may be used to generate a test that allows for
detection of the species of interest. The present invention provides a
device that is able to detect ligands binding to proteins, for example.
The protein is covalently attached to a vibrating carbon fiber and the
frequency and amplitude of the vibrations are monitored. The fiber
changes its frequency and amplitude of vibration as the ligand binds,
thus providing a detection system to monitor this effect. The detection
of a biological contaminant, like a bacterium, is most useful if the
presence of >100 CFU's of the bacteria may be detected within 15
minutes with the medium of the assay being still or flowing liquid or
air. Such a system has far reaching potential uses. For example,
attaching Bovine Serum Albumin (BSA) to a carbon fiber allows for several
size agents to be monitored. Attachment of an antibody to the carbon
allows for detection of a microbe. Appropriate experiments run with
controls for viscosity and non-specific binding allow one to ascertain
the range of agents and sensitivity of the test.

[0041]Thus, a particularly promising idea associated with the present
invention is to attach protein A and G to the sensor (i.e. fiber).
Protein A and G has many Fc receptor sites and most all antibodies have
Fc receptors. Therefore, this makes it relatively easy to bind an
antibody to protein A and G. Effort is spent modifying protein A and G to
the fiber(s) and then anyone may attach their own antibody and make this
specific for what they want to capture, collect, and/or detect. The
standing wave probes of the present invention may then be used to rapidly
collect, concentrate, and/or bind antigens to the fiber as long as the
fiber is modified. The transducer on the back end (i.e. tuning fork) may
be used to detect mass changes via resonance frequencies. Also,
fluorescent techniques may be used as a form of detection (i.e. if the
antibody fluoresces when present) when antigens bind to the fiber. A
final method of sensing is to engineer the fiber to detect and sense mass
changes itself. It should be noted that, in this exemplary application,
the device may work where a ligand is on the probe or a receptor is on
the probe. The detection is for what is not covalently attached and is in
the surrounding media. The receptor may be a protein, an antibody, or any
other recognition unit that will recognize a ligand. In this case, a
ligand may be a small molecule, a protein or a organism like a bacteria
or virus. The ability to detect may also allow for quantitation of the
agent to be detected.

Example--Liquid Handling and Micromixing for High Throughput Drug
Discovery

[0042]As the population ages, there is a pressing need for new treatments,
therefore the pharmaceutical industry is fervently increasing the number
of new chemical entities that may potentially be turned into drugs. As
the number of potential drug candidates (or leads) increases, the need
for high throughput screening (HTS) will grow in parallel, making it
necessary to have a highly automated HTS system. HTS enables researchers
to rapidly conduct thousands of pharmacological, genetic, and biochemical
tests to identity potential new drug candidates (or leads). The process
provides the ability to identify parameters such as genes and active
compounds, and thus enables faster insight to drug discovery and
understanding the interactions of a biochemical process. Screening
stations often comprise multiple instrumented platforms for robotic
handling, dispensing, mixing, and detection. New instrumentation,
including systems such as those for liquid and gas handling and
detection, is one of the most crucial elements for the advance of
automated HTS.

[0043]The HTS market represents a highly technological activity and
pharma/biotech industries continue to face an increase in lead compounds.
HTS and ultra-high throughput screening (UHTS) are emerging, requiring
thousands if not millions of compounds to be tested each week. The
pharmaceutical industry currently has a pressing need for improvement in
HTS technology. Three key technological areas are critical to advancing
the state of HTS. These include: 1) automation, 2) miniaturization, and
3) cost savings. Faster automation has a direct correlation to faster
workflow for drug discovery and minimizing manual interventions is a key
step. Miniaturization, the introduction of systems capable of handling
nanoliter and picoliter sample quantities (i.e. microassay technology) is
desired by companies, but is currently not commercially available. Such a
capability will provide distinct advantages in reducing the cost per
assay, increasing assay sensitivity, specificity, and speed. Finally, the
number of chemical/biological assays continues to rise and the expenses
in consumables and supplies continue to grow as well. Therefore, the
industry continues to look for ways of significantly lowering the total
cost of generating each HTS data point. As a result, the HTS industry
continues to look for novel technologies that provide advanced
automation, miniaturization, and that reduce the cost per data point.

[0044]A mesoscale (i.e. milliscale), microscale, nanoscale, or picoscale
liquid or gas handling and micromixing probe is possible using the
standing wave probe 10, 20 of the present invention, addressing
miniaturization, cost savings, and faster automation in a single
platform--additionally, it may be self-cleaning. For example, this
technology utilizes a 7 μm microscale fiber 12 (with free lengths
ranging from 1 to 5 mm) attached to a mechanical oscillator 14. Once the
oscillator 14 is active, a pronounced mechanical wave operating at 32 kHz
is induced in the fiber 12. The oscillator 14 also serves as a transducer
with the capability to monitor precise mechanical changes in the standing
wave 16. This technology has demonstrated nano-Newton force detection 1)
when used as a tactile device for nanoscale dimensional measurements, 2)
has been employed as a self sensing pick and place tool to pick up and
weigh small mass samples such as picoliter droplets, 3) has been shown to
concentrate particles and is currently being investigated for use in
Raman spectroscopy, and 4) has demonstrated the capability to be used as
a biosensor.

[0045]Using a modified standing wave probe 10, 20 consisting of a pair of
microscale fibers 12 manufactured such that the gap between the fibers 12
(<100 microns) will cause fluid to wick between the rods 12, accurate
measurement and dispensing capability is achieved. The pair of fibers 12
and a resonator 14 may be attached to a high speed nanopositioning device
or the like. First, the oscillator 14 is activated, generating a standing
wave 16 in the microscale fiber 12. Once the fiber 12 contacts the liquid
or gas, the oscillator 14 immediately registers a response (i.e. in
milliseconds) and a null position is set. Now the nanopositioner may
controllably immerse the fibers 12 to a specified depth. Once the
oscillator 14 is turned off, the probe is extracted from the fluid
containing a small volume of fluid in the gap between the fibers 12. The
amount of fluid wicked between the fibers 12 is highly deterministic for
two reasons. First, the depth the fiber 12 is inserted into the fluid is
always highly controlled. Second, once the probe 10, 20 is extracted from
the fluid, the probe 10, 20 may operate with a low standing wave 16 (i.e.
with a low enough energy to prevent fluid from releasing) and measure the
mass of the liquid or gas, providing a fluid metering tool. The probe 10,
20 is then automatically translated to the next sequence and immersed
into the target liquid or gas. Once immersed, a standing wave 16 is
generated in the fibers 12, thus causing a mixing reaction to occur. Once
a homogenous mixture occurs, the probe 10, 20 is removed and immersed
into a cleaning fluid and activated again.

[0046]Within the HTS market, instruments used in drug discovery process
are segmented into liquid handling robots, microplate readers, consumable
supplies, imaging technology, microarray readers, microplate washers, and
handling and software for data analysis. The technology of the present
invention differentiates in two critical areas for liquid and gas
handling and mixing. A lot of technologies traditionally dispense liquids
through micropipettes into microplates, which are then placed on a shaker
to mix. The drive towards miniaturization of assays for HTS requires
precise, low-volume liquid-dispensing instrumentation. Over the last
several years, automated instrumentation capable of handling low volume
384-well plates and well plates with 1,536 wells have entered labs.
Liquid handling typically comprises a variety of tools such as pipettes,
harvesters, plate and strip washers, and dispensing systems. Syringe
technology is the most traditional source-to-destination fluid transfer
methods and remains cost effective and versatile. Pipettors have been
shown to be capable of accurately metering volumes as low as 100 nL, but
they have difficulty of transferring smaller volumes to the destination
without contact. Another more traditional liquid transfer technology is
the "pin tool", which allows fluid to wick onto the ends of metallic pins
and then transfers the liquid to the targeted area. The size of the
droplet is controlled by the cross sectional area of the pin with the
smallest pin (with a diameter of 0.229 mm) providing a 7 nL dispensed
droplet. The disadvantage with this method is that it cannot monitor the
droplet size to ensure the exact amount of liquid transferred, it is not
versatile in that it cannot change the size of the droplet, and there is
no mixing capability.

[0047]More recently, liquid handling technology has trended toward
piezoelectric, ink-jet, or solenoid actuation and away from traditional
syringe technology. However, these dispensing technologies do not meter
fluids. Additionally, these systems require substantial hardware and can
therefore be very expensive if many channels are incorporated in the
instrument. The systems function by using syringes that aspirate a
certain amount of reagent and then dispense that amount. Some systems use
a flow-through type dispenser, which does not require aspirating because
it uses pressure to push the liquid through valves that open and shut to
dispense the liquid. None of these dispensing tools have the ability to
provide liquid transfer and liquid metering, nor do they provide active
mixing capability for the samples. Finally, these technologies are
challenging to miniaturize for microassays.

[0048]One distinct challenge in miniaturizing HTS systems is to be able to
mix microfluids and solids, gasses, etc. Achieving the criteria of fast,
efficient, and thorough (i.e. no concentration gradients) mixing has
proven to be one of the main bottlenecks to achieving the potential
benefits that microfluidics has to offer. Biological reactions which
occur at the macroscale almost always involve the mixing of the
biological specimen with reagents. In these systems, rapid homogeneous
mixing of liquid solutions is considered one of the most challenging
issues. This is particularly true for solution streams containing
micromolecules (i.e. DNA, cells, proteins, etc.) or large particles (i.e.
bacteria) which have diffusion coefficients orders of magnitude lower
than most fluids. Concentration gradients between two fluids being mixed
can affect the outcome of the process. Mixing (whether in the
lab-on-a-chip (LOC) system or applied to conventional processes) can
accelerate hybridization kinetics and improve uniformity of the
hybridization in a shallow chamber (i.e. a PCR tube, well plate, or
microfluidic chamber). Particular difficulties arise where small, finite
volumes of liquids must be mixed, such as in the case of microassays. The
crux of the problem lies in the fact that the typical Reynolds number for
micron-scale fluidic systems is small, usually considerably less than
1000, and this means that the traditional phenomena available for mixing
(that of turbulent velocity motion) is not available since the fluid flow
is laminar. Thus, only molecular diffusion is available for mixing. From
dimensional analysis, typical timescales for laminar diffusion are given
by Tlam=D/L2 where D is the diffusion coefficient and L is the
characteristic length scale of the system. For a typical biological
system (e.g. mixing a moderately-sized protein in a 100 micron channel),
Tlam is ˜500 sec, far too long for any practical application.
Proposed solutions to micromixing are divided into passive and active
methods. Passive methods require no input energy and achieve enhanced
mixing either by elongation of laminar interfaces such as serpentine
channels or by a "divide-and-conquer" scheme in which the two streams are
divided into multiple parallel paths and mixed in sub-streams. A second
approach is to induce chaotic mixing through geometric complexity, such
as a 3D channel geometry, or by textured surfaces. These techniques
improve the mixing efficiency and speed when compared with plane channel
geometries, but still require relatively large Reynolds numbers (to
induce the necessary secondary flows required for chaotic motion) and
still require flow-through systems rather than residential microreactors.
Batch micromixing cases tend to be more applicable where, for example, in
pathological screening tests a drop of patients blood is mixed with a
reagent for screening type pathology tests or for biochips requiring DNA
hybridization. The mixing should occur using a simple, economical device
enabling cost effective HTS processes feasible, point-of-care
immunoassays, and such applications typically favor active mixing
approaches.

[0049]Active mixers use some form of energy input to induce fluid motion
which enhances mixing, a manifold of approaches have been proposed
including electrokinetic, magnetic beads, external pumping motion, and
even live bacteria. A complication to active mixing is that at low
Reynolds numbers, any unsteady motion introduced into the microsystem is
often reversible, and thus any mechanisms that might otherwise stir the
fluid in a macroscopic configuration often has little added benefit at
small scale. To address this, chaotic mixing strategies or the use of
inherent instabilities are often adopted. Nevertheless, a significant
drawback of many previously-demonstrated systems is that many of these
active systems require that either a foreign substance be present in the
fluid (e.g. magnetic beads, dielectric particles, etc.) or that the fluid
have some rather specific properties (pH, conductivity, thermal
coefficient of density, etc.).

[0050]The challenge, thus, is to design a system that is capable of
receiving a single drop, without a complex liquid feeding system, and to
mix the drop efficiently enough with the reagent for any binding
reactions to occur over a timescale of tens of seconds rather than hours.
This requires implementing a simple cost effective active mixing
mechanism that does not cause damage to the biological samples or require
the introduction of foreign agents into the fluid stream. This is the
technology offered by the present invention.

[0051]By coupling the fiber 12 to a mechanical resonator 14 having a high
mechanical Q, an unprecedented type of energy in the form of a standing
wave 16 is propagated along the fiber 12, sustained, and finally used for
environmental sensing. The geometric volume of the fiber 12 compared to
the elastic deformation propagated in the fiber 12 exhibits an
unprecedented amount of potential and kinematic energy occurring in a
small form factor. The standing wave's amplitude and mode shape are
dependent upon many factors including: 1) the fiber's material properties
and geometric scaling, 2) the input drive frequency and oscillation
amplitude, and, finally, 3) the damping properties due to the bonding
agent between the fiber and oscillator. The pronounced wave pattern is
exhibited in a one dimensional fashion and the amplitude may vary
depending upon the input drive frequency or peak-peak drive voltage
transferred to the tuning fork 14.

[0052]As described above, the standing wave technology may be implemented
to sense environmental interactions. The tuning fork resonators 14
provide electrodes for actuation as well as sensing the mechanical
response from the resonator 14. By sweeping through drive frequencies,
the output sensor signal compared to the drive voltage will shift by 180
degrees when passing through the natural frequency. This shift in phase
and magnitude response may then be used as a form of measurement for a
variety of parameters including dimensional measurements and force. A
variety of signal conditioning electronics have been developed and used
to extract precision signals.

Example--Viscometry and Rheology of Microsamples

[0053]The measurement of the physical properties of liquids and gasses,
specifically the viscosity and rheological behavior of materials, is very
important for process engineering and analytical research. Measurements
of viscosity during processing, manufacturing, and production is
necessary across a wide range of industries such as biochemistry, fuel
oil production, and research including biofuels, bodily fluid/blood
analysis, polymer processing, food production and research, biomedical
applications, such as blood analysis, and in metals processing.
Additionally, in situations, specifically in the fields of biology and
medicine (e.g. clinical laboratory testing) the amount of liquid
available for measurement is quite small or the cost of the liquids is
high resulting in a desire to use small quantities whenever possible.

[0054]In the viscometry and rheology equipment markets the demand for
viscometers and rheometers is driven by the need to determine flow
behavior of fluids. Viscometers enable the ability to measure viscous
properties of fluids such as liquids, semi-solids, and gasses either in
an industrial setting or in a laboratory environment. This is a necessary
quality control step in the production of most fluids, creams, and gels
in order to ensure product consistency and quality to fulfill customer
demands, and therefore these measurements influence cost efficiency to a
great extent. There are so many varied techniques to make viscosity and
rheology measurements that it becomes imperative to choose the most
suitable instrument for use in specific applications. However, there is a
lack of technological innovation in this area which restrains growth of
the market because there has been little or no innovation for nearly half
a century. Nonetheless, manufacturers have been striving to improve
product performance by focusing on automation, user-friendly instruments,
and reliability and accuracy. There is a growing need for a device
designed to measure microsamples (on the order of microliters) to address
drug discovery, biotech, and medical application markets. A viscosity
measurement technology that could use less than 20 μL sample size and
be configured as a laboratory instrument or a flow through measurement
device is unique.

[0055]The standing wave probes 10, 20 of the present invention may be used
as a mesoscale (i.e. milliscale), microscale, nanoscale, or picoscale
viscometry sensor, with the potential to quantify both bulk fluids and
microfluids in a production or laboratory environment. For example, the
concept again uses a 7 μm microscale fiber 12 (with free lengths
ranging from 1 to 5 mm) attached to a mechanical oscillator 14. Once the
oscillator 14 is active, a pronounced mechanical wave operating at 32 KHz
is induced in the fiber 12. The oscillator 14 also serves as a transducer
with the capability to monitor small mechanical changes in the standing
wave 16. This technique has the benefit that it is simple, inexpensive,
quick, and can work on small sample volumes (microliters) as well as bulk
samples.

[0056]Viscosity is a property of a fluid that offers resistance to flow.
Therefore, it is the ratio of the shearing stress to the velocity
gradient in a fluid. Most fluids, such as air and water, exhibit a linear
relationship between shear stress versus shear rate. When plotting this
relationship, the slope is the viscosity of the fluid. Additionally, the
viscosity is a function of the temperature. One common example is
lubricants, whose viscosity can double with a change of only 5° C.
For some fluids, it is a constant over a wide range of shear rates.
Fluids with a constant viscosity (i.e. a linear relationship) are called
Newtonian. Any fluid that does not have this linear relationship is
called non-Newtonian, that is the viscosity of the fluid is dependent on
shear rate. Their viscosity cannot be described by a single number.
Rheology is the study of the behavior of these types of fluids and their
dependence on shear. There is actually more than one quantity that is
called viscosity. The most common and the one described above is often
referred to as dynamic viscosity, absolute viscosity, or simply
viscosity. The other quantity, called kinematic viscosity, is the ratio
of the viscosity of a fluid to its density. It is frequently measured
using a device called a capillary viscometer and measured in units called
centiPoise (cP).

[0057]For the past 50 years, viscometry instrumentation and methodologies
have remained predominantly unchanged. Technologies include cup and drop,
capillary and rotating element viscometers. The rotating element
viscometer gives quantitative results for a limited measurement range and
accuracy. Viscosity measurements on the these traditional technologies
are tedious, and in many instances the flow time is lengthy. More
recently a number of resonance based viscosity sensing devices have been
introduced in the literature, several of which have become commercial
products in various forms and sizes and targeting different application
areas. These methods operate by measuring the damping of an
electromechanical resonator immersed in a fluid sample. For example,
larger damping on the resonator indicates higher viscosity.

[0058]However, there are several downfalls to directly inserting the
tuning fork into the liquid. One disadvantage of this technique is the
lack of a defined shear field which makes it unsuitable for measuring
viscosity of fluids due to unknown flow behavior. Additionally, tuning
fork resonators fall short when measuring viscosity and density of
electrolytes (tap water and low purity grade alcohols for example)
because of the electric field generated in the liquid and coating the
tuning fork does not solve the problem. Another complication is that the
quality factor (Q) which directly affects sensitivity, decreased from
˜7000 in air to as low as 10 in liquid. One proposed solution is to
increase the drive voltage to as much as 1500 V, but this is undesirable.
The approach of the present invention also uses high frequency vibrations
created by a tuning fork resonator, but the boundary conditions,
measurement techniques, and mechanical waves are distinctly different.
However, the success of using tuning fork resonators substantiates the
validity of this methodology. Because in the methodology the resonator
does not make direct contact with the fluid, it does not experience the
reduced Q and therefore the method provides better sensitivity compared
with the methods described above.

[0059]Again, by coupling the fiber 12 to a mechanical resonator 14 having
a high mechanical Q, an unprecedented type of energy in the form of a
standing wave 16 is propagated along the fiber 12, sustained, and finally
used for environmental sensing. The geometric volume of the fiber 12
compared to the elastic deformation propagated in the fiber 12 exhibits
an unprecedented amount of potential and kinematic energy occurring in a
small form factor. The standing wave's amplitude and mode shape are
dependent upon many factors including: 1) the fiber's material properties
and geometric scaling, 2) the input drive frequency and oscillation
amplitude, and, finally, 3) the damping properties due to the bonding
agent between the fiber and oscillator. The pronounced wave pattern is
exhibited in a one dimensional fashion and the amplitude may vary
depending upon the input drive frequency or peak-peak drive voltage
transferred to the tuning fork 14.

[0060]As described above, the standing wave technology may be implemented
to sense environmental interactions. The tuning fork resonators 14
provide electrodes for actuation as well as sensing the mechanical
response from the resonator 14. By sweeping through drive frequencies,
the output sensor signal compared to the drive voltage will shift by 180
degrees when passing through the natural frequency. This shift in phase
and magnitude response may then be used as a form of measurement for a
variety of parameters including dimensional measurements and force. A
variety of signal conditioning electronics including lock-in amplifiers
and phase lock loop electronics have been developed and used to extract
precision signals.

[0061]The equivalent circuit for a tuning fork includes two parallel
impedances. The first is the static capacitance, C0, of the tuning fork,
and the second is the tuning fork dynamics, represented by the three
elements C1, the compliance, L1, the mass, and R1, the dissipation of the
fork. A high aspect ratio microscale fiber coupled to a mechanical
resonator would have the same basic model with different values for the
circuit elements. The effective result is a more sensitive system based
on the fact that the fiber will absorb more energy because it vibrates at
a much higher amplitude than the motion of the tuning fork tines. This
exemplary model can be extended to include an additional impedance ZL
produced by the surrounding liquid. This impedance is related to the
operational frequency, liquid density, and liquid viscosity.

[0062]In other methodologies, when the tuning fork makes contact with the
liquid, the static capacitance, C0, will also be affected by the
electrical properties of the surrounding liquid. This complication by the
methodology of the present invention. If the tuning fork is submerged in
the liquid, the signal is significantly damped and the signal to noise
will decrease significantly making any noise in the system a significant
contribution in the measurement, decreasing the accuracy of the
methodology.

[0063]It is well established that a higher mechanical `Q` oscillator
relates to higher sensitivity and even feasibility for advanced
applications. The `Q` is a dimensionless value that compares the
oscillator's amplitude to the resonance frequency. The oscillator's input
and output signals are compared for shifts in resonant frequency,
magnitude, and phase. If the oscillator has a high Q, a small shift in
frequency away from resonance will result in a rapid decay of the output
signal. Conversely, a low Q will result in a small rate of decay in
electrical signal. If the sensor's signal change decreases below the RMS
noise then the sensor is simply unable to detect. Therefore, the general
rule is to design resonators with higher mechanical Q's for realizing
highly precise sensing. The oscillators typically reported have
significantly low mechanical Q where the best values do not exceed 100.
However, the Q value for the standing wave sensor while measuring in
liquid is a factor of 20-30 times higher. The fundamental difference is
the conventional oscillators are partially or fully immersed in the
liquid and are therefore highly damped which directly affects the
sensitivity. The present invention, on the other hand, immerses the
mesoscale (i.e. milliscale), microscale, nanoscale, or picoscale fiber in
the fluid. Although the fiber is small in comparison to the tuning fork,
very small changes in frequency and magnitude may be resolved, thereby
leading to precise mesoscale (i.e. milliscale), microscale, nanoscale, or
picoscale sensor for fluid property measurements.

[0064]Although the present invention is illustrated and described herein
with reference to preferred embodiments and specific examples thereof, it
will be readily apparent to those of ordinary skill in the art that other
embodiments and examples may perform similar functions and/or achieve
like results. All such equivalent embodiments and examples are within the
spirit and scope of the present invention, are contemplated thereby, and
are intended to be covered by the following claims.